Never mind about converting the bytes to something a human can read - which is the purpose of Serial.prin().
Just save the bytes into an array
byte myArray[5][12]; // creates 5 arrays each with 12 bytes (I hope)
for (byte x = 0 ; x < 12 ; x++)
{
myArray[0][x] = nano.msg[31 + x]; // stores the values in the first of the 5 rows
}
...R